1. Field of the Invention
The present invention relates to a mounting configuration for a chain guide of a cam chain for transmitting power to a power valve system of an internal combustion engine.
2. Description of Background Art
FIG. 13 is a front view showing one example of a cam chain and a chain guide of an internal combustion engine according to the background art. A cam chain 03 is stretched over between a crank shaft sprocket 01 and a cam shaft sprocket 02 to transmit rotation of a crank shaft 01a to a cam shaft 02a. Numeral 04 designates a crank casing; 05 is a cylinder block; 06 is a cylinder head; and 07 is a head cover. These components are fixedly assembled in sequence.
Numeral 08 designates a chain guide disposed along the cam chain 03. A first protrusion 08a is provided on a lower end of the chain guide 08 and is fitted into a first locating groove 09 provided in the vicinity of the crank shaft 01a in the crank casing 04. Furthermnore, a second protrusion 08b is provided at an upper part of the chain guide 08 and is fitted into a second locating groove 010 provided in an upper surface of the cylinder block 05. Numeral 011 designates a chain tensioner disposed along the cam chain 03 at a position opposite to the chain guide 08. A lower end of the chain tensions 011 is pivotally supported by a shaft 011a, and an upper part of the chain tensions 011 is pressed against the cam chain 03 by a hydraulic device 012 so as to suppress looseness of the cam chain 03.
In an overhead valve system, a cam shaft is provided externally of a cylinder bore to operate a intake/exhaust valve through a push rod and a rocker arm by rotation of the cam shaft. Since a position of the cam shaft is low and is greatly displaced from a portion of the internal combustion engine directly above the crank shaft, it is difficult to provide a chain guide locating groove in the upper surface of the cylinder block. Furthermore, since the rotational direction of the cam chain, i.e., the longitudinal direction of the chain guide is deviated from the vertical direction, if the chain guide is fixed in advance when the cylinder block is mounted along a stud bolt embedded in the crank casing, the upper end of the chain guide interferes with the inner wall of the cylinder block so that the cylinder block cannot be mounted.
For solving the above-described problem, the present invention provides a mounting device for a cam chain guide for an internal combustion engine, wherein rotation of a crank shaft is transmitted to a cam shaft provided externally of a cylinder bore by a cam chain to operate a supply-exhaust valve through a push rod and a rocker arm. In addition, a first protrusion provided in the vicinity of a lower end of a chain guide is fitted into a first locating groove provided in the vicinity of the crank shaft in a crank casing, and a second protrusion provided in the vicinity of an upper end of the chain guide is fitted into a second locating groove provided in a lower surface of a cylinder block of the internal combustion engine. The second locating groove is gradually enlarged from an inner position toward the opening thereof.
According to the present invention configured as described above, since the second locating groove is provided in the lower surface of the cylinder block, even if the position of the cam shaft is low and greatly deviated from a portion of the internal combustion engine directly above the crank shaft, the position of the upper locating groove can be freely selected. Furthermore, since the second locating groove is gradually enlarged toward the opening from an inner fixed position of the second protrusion of the chain guide, when the chain guide and the cylinder block are mounted, the protrusion can be easily inserted into the locating groove after passing by the location of interference with the cylinder block and therefore making mounting simple.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.